Mechanical repair of damaged airfoil structure

ABSTRACT

A process is provided for repairing an airfoil structure adapted for use in a gas turbine engine comprising: providing an airfoil structure having a section with a defect; removing airfoil structure material comprising the section with the defect such that a through hole is created; providing a replacement element; providing interlocking structure; positioning the replacement element relative to the through hole; and securing the replacement element to the airfoil structure via the interlocking structure such that the through hole is covered.

FIELD OF THE INVENTION

The present disclosure relates to a process for repairing a damaged section of a gas turbine engine airfoil structure by mechanically coupling a replacement element to the airfoil structure.

BACKGROUND OF THE INVENTION

There are a series of rows of stationary vanes and rotating blades in a turbine section of a gas turbine engine. The blades are coupled to a rotor disc assembly. Hot working gases travel to the rows of blades. As the working gases expand through the turbine, the working gases cause the blades and, hence, the rotor disc assembly to rotate.

An airfoil structure may comprise a stationary vane or a rotatable blade. The stationary vane may comprise an airfoil, a platform coupled to each end of the airfoil and rails extending from the platforms. The blade may comprise an airfoil, a platform coupled to a lower end of the airfoil and a root extending from the platform. During engine operation, a vane or a blade may become worn or damaged. Known techniques for repairing a worn or damaged vane or blade comprise welding, brazing or transient liquid phase bonding. For example, filler material may be welded to a damaged section.

Thereafter, the repaired section may be heat treated. However, because vanes and blades are typically made from superalloys, repair welding often produces liquation cracking and post weld heat treatment often produces strain age cracking.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present disclosure, a process is provided for repairing an airfoil structure adapted for use in a gas turbine engine comprising: providing an airfoil structure having a section with a defect; removing airfoil structure material comprising the section with the defect such that a through hole is created; providing a replacement element; providing interlocking structure; positioned the replacement element relative to the through hole; and securing the replacement element to the airfoil structure via the interlocking structure such that the through hole is covered.

Removing may comprise forming a through hole comprising a first outer section and a second inner section. The first section may have a diameter greater than that of the second section.

The replacement element may comprise a first outer portion and a second inner portion. The first portion may have a diameter slightly less than the diameter of the through hole first section and the second portion may have a diameter slightly less than the diameter of the through hole second section. The first outer portion may be received in the through hole first section and the second inner portion may be received in the through hole second section.

The interlocking structure may comprise threads on the replacement element and a section of the airfoil structure adjacent the through hole.

The process may further comprise sealing the replacement element to the airfoil structure.

The interlocking structure may comprise a pin positioned through the replacement element and a section of the airfoil structure adjacent the through hole.

The process may further comprise sealing the replacement element and the pin to the airfoil structure.

The pin may be threaded.

The pin may be positioned at a non-orthogonal angle to an outer surface of the replacement element.

The airfoil structure may comprise a vane or a blade.

The replacement element may comprise a main body portion and the interlocking structure may comprise at least one tongue extending from the main body portion. The process may further comprise forming at least one groove in a section of the airfoil structure adjacent the through hole. The tongue is adapted to be received in the groove.

The interlocking structure may comprise first, second, third and fourth tongues extending out from the main body portion. The process may comprise forming first, second, third and fourth grooves in the airfoil structure section adjacent the through hole.

The first, second, third and fourth tongues may have curved shapes and the first, second, third and fourth grooves may have curved shapes.

Positioning may comprise positioning the replacement element upside down relative to an outer surface of the airfoil structure and securing may comprise rotating the replacement element 180 degrees such that the first and second tongues move through the third and fourth grooves and then into the first and second grooves and the third and fourth tongues move into the third and fourth grooves when the first and second tongues move into the first and second grooves.

In accordance with a second aspect of the present disclosure, a repaired airfoil structure is provided comprising: an airfoil structure having a through hole formed therein so as to remove a section with a defect; a replacement element positioned in the through hole; and interlocking structure to mechanically couple the replacement element to the airfoil structure.

The interlocking structure may comprise a pin positioned through the replacement element and a section adjacent the through hole.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed that the present invention will be better understood from the following description in conjunction with the accompanying Drawing Figures, in which like reference numerals identify like elements, and wherein:

FIG. 1 illustrates a vane having an airfoil with a defect;

FIG. 2 illustrates the vane in FIG. 1 including a through hole formed when a section of the airfoil including the defect is removed;

FIG. 3 is a side view of a replacement element of a first embodiment of the present disclosure;

FIG. 4 is a top view of the replacement element illustrated in FIG. 3;

FIG. 5 is a cross sectional view illustrating the replacement element fitted into a through hole in the vane;

FIG. 6 is front view of a curved portion of an airfoil of a vane;

FIG. 7 is a view taken along view line 7-7 in FIG. 6;

FIG. 8 is a top view of a replacement element of a further embodiment of the present disclosure;

FIG. 9 is a side view of the replacement element illustrated in FIG. 8;

FIG. 10 is an end view of the replacement element illustrated in FIGS. 8 and 9;

FIG. 11 is a view of a through hole in an airfoil formed in accordance with a further embodiment of the present disclosure; and

FIGS. 12A-12D illustrate steps for assembling the replacement element of FIG. 8 to the airfoil illustrated in FIG. 11.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the preferred embodiment, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration, and not by way of limitation, a specific preferred embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and that changes may be made without departing from the spirit and scope of the present invention.

An airfoil structure may comprise a stationary vane or a rotatable blade for use in a gas turbine engine. An example stationary vane 10 is illustrated in FIGS. 1 and 2. The vane 10 comprises an airfoil 12, first and second platforms 14A and 14B coupled to opposing ends of the airfoil 12 and rails 16 extending outward from the platforms 14A and 14B. A blade (not shown) may comprise an airfoil, a platform coupled to a lower end of the airfoil and a root extending from the platform.

There are a series of rows of stationary vanes and rotating blades in a turbine section of a gas turbine engine. The blades are coupled to a rotor disc assembly. Hot working gases travel to the rows of blades. As the working gases expand through the turbine, the working gases cause the blades and, hence, the rotor disc assembly to rotate.

During gas turbine engine operation, one or more of the vanes and blades may become worn or damaged. In accordance with the present disclosure, a process is provided for repairing an airfoil structure adapted for use in a gas turbine engine. While the process of the present disclosure will be discussed herein in the context of repairing a vane, the process of the present disclosure may also be used to repair a defect in an airfoil structure comprising a blade.

In FIG. 1, a section 12A of the vane airfoil 12 is shown having a defect D. The defect D may comprise worn away (missing) material, burned (oxidized or melted) material, corroded material, cracked material, or damage from foreign object impact.

The defect D is repaired in accordance with a first embodiment of this disclosure as follows. Material including the defect D is removed, i.e., the section 12A with the defect D is removed, using a conventional cutting process, such that a through hole 120 is created in the airfoil 12, see FIGS. 2 and 5. The cutting process may comprise machining by grinding, turning, milling, routing, drilling, water jet cutting, laser cutting or electro-discharge machining. In the illustrated embodiment, the through hole 120 comprises a first outer section 120A and a second inner section 120B, see FIGS. 2 and 5. The first outer section 120A has a first diameter D₁ and the second inner section 120B has a second diameter D₂. In the illustrated embodiment, the first diameter D₁ is greater than the second diameter D₂.

Next, a replacement element 30 is provided to fill and seal the through hole 120, see FIGS. 3-5. Also provided is interlocking structure, which, in the illustrated embodiment, comprises a pin 40, see FIG. 5. The replacement element 30 comprises a first outer portion 30A and a second inner portion 30B. The first portion 30A has a third diameter D₃ slightly less than the first diameter D₁ of the through hole first section 120A and the second inner portion 30B has a fourth diameter D₄ slightly less than the second diameter D₂ of the through hole second section 120B, see FIGS. 3 and 5. The pin 40 has a cylindrical shape in the illustrated embodiment.

The replacement element 30 is fitted into the through hole 120 such that the first outer portion 30A is received in the through hole first section 120A and the second inner portion 30B is received in the through hole second section 120B.

In the illustrated embodiment, a first bore 30C is formed in the replacement element first outer portion 30A, see FIGS. 4 and 5. The bore 30C does not extend through the replacement element second inner portion 30B, see FIG. 4. A second bore 12B is formed in a section 12C of the airfoil 12 adjacent the through hole 120, see FIG. 5. In the illustrated embodiment, the first and second bores 30C and 12B are aligned with one another. So as to secure the replacement element 30 to the airfoil 12, the pin 40 is press fitted into the bores 30C and 12B such that a friction fit is created between the pin 40 and each of the replacement element 30 and the airfoil 12.

In the illustrated embodiment, the pin 40 is positioned relative to the replacement element 30 such that its longitudinal axis is generally orthogonal to an outer surface 30D of the replacement element 30. However, it is also contemplated that the first and second bores 30C and 12B may be formed in the replacement element 30 and the airfoil 12 such that the pin 40 extends at a non-orthogonal angle, e.g., 45 degrees, to the outer surface 30D of the replacement element 30. It is further contemplated that threads (not shown) may be provided on the pin 40 and the structure of the replacement element 30 defining the bore 30C and the structure of the airfoil 12 defining the bore 12B. Hence, instead of using a friction or press fit to secure the pin 40 to the replacement element 30 and the airfoil 12, a threaded connection may be used.

Instead of using a pin 40 to secure the replacement element 30 to the airfoil 12, it is further contemplated that threads may be provided on the replacement element 30 and the structure defining the through hole 120 such that the replacement element 30 may be threadedly coupled to the airfoil 12. The threads on the replacement element 30 and the structure defining the through hole 120 define interlocking structure in this embodiment.

After the replacement element 30 has been assembled and secured to the airfoil 12, the replacement element 30 and the pin 40 are further secured to the airfoil 12 via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may be effecting during the process of assembling the replacement element 30 and the pin 40 to the airfoil 12. In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element 30 and/or the pin 40.

The process of the present invention may also be used to repair a damaged section on a curved portion 12D, e.g., a leading or trailing edge, of the airfoil 12, see FIGS. 6 and 7. The airfoil 12 has a wall 320. A section of the wall 320 having a defect is removed to create a through hole 220. A section 320A of the airfoil wall 320 surrounding the through hole 220 is notched so as to have a first thickness T₁, which is less than a second thickness T₂ of sections 320B of the airfoil wall 320 that are not notched. A replacement element 230 is then fitted over the through hole 220 and a pin 240 is press fit into bores 230A and 320C provided in the replacement element 230 and the airfoil wall section 320A so as to secure the replacement element 230 to the airfoil 12, see FIG. 7.

After the assembly process of the replacement element 230 and the pin 240 to the airfoil 12, the replacement element 230 and pin 240 are further secured to the airfoil 12 via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may be effecting during the process of assembling the replacement element 230 and the pin 240 to the airfoil 12. In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element 230 and/or the pin 240.

In accordance with a further embodiment of the present disclosure, a defect in an airfoil 412 is repaired as follows. Material is removed, i.e., a section with a defect is removed, using a conventional cutting process, such that a through hole 420 is created in the airfoil 12, see FIG. 11. Curved end walls 412A and 412B and generally planar side walls 412C and 412D of the airfoil 412 define the through hole 420. First, second, third and fourth curved engagement grooves 414A-414D are formed in airfoil structure adjacent the through hole 420 such that the grooves 414A-414D extend inwardly from the airfoil side walls 412C and 412D. The grooves 414A-414D may be formed via conventional milling cutters or electro-discharge machining. Further, the grooves 414A-414D may have a cross sectional shape of a square, semi-circle or dove-tail.

Next, a replacement element 430 is provided to fill and seal the through hole 420, see FIGS. 8-10 and 12A-12D. The replacement element 430 may comprise a main body portion 430A having generally curved end walls 430B and 430C, generally planar side walls 430D and 430E and generally planar upper and lower surfaces 430F and 430G, see FIGS. 8-10. The curvature of the main body portion curved end walls 430A and 430B is generally the same as the curvature of the curved end walls 412A and 412B of the airfoil structure defining the through hole 420.

The interlocking structure comprises first, second, third and fourth curved tongues 440A-440D extending from the main body portion 430A of the replacement element 430, see FIGS. 8-10. The curvature of the tongues 440A-440D is generally the same as the curvature of the curved engagement grooves 414A-414D, see FIGS. 8-11 and 12A-12D. Further, the tongues 440A-440D may have a cross sectional shape matching the cross sectional shape of the grooves 414A-414D.

To assemble and secure the replacement element 430 to the airfoil 412, the replacement element 430 is initially positioned upside down relative to an outer surface 413 of the airfoil structure 412, see FIG. 12A. The replacement element 430 is then rotated 180 degrees. In FIG. 12B, the replacement element 430 is shown rotated about 30 degrees from its position shown in FIG. 12A such that the first and second tongues 440A and 440B are located respectively in the third and fourth curved engagement grooves 414C and 414D. In FIG. 12C, the replacement element 430 is shown rotated about 90 degrees from its position shown in FIG. 12A such that the first and second tongues 440A and 440B have moved out of the third and fourth curved engagement grooves 414C and 414D. In FIG. 12D, the replacement element 430 is shown rotated about 170 degrees from its position shown in FIG. 12A such that the first and second tongues 440A and 440B have moved respectively into the first and second curved engagement grooves 414A and 414B and the third and fourth tongues 440C and 440D have moved into the third and fourth curved engagement grooves 414C and 414D. When the replacement element 430 has rotated 180 degrees from its position shown in FIG. 12A, the first, second, third and fourth tongues 440A-440D are respectfully fully engaged with and positioned within the curved engagement grooves 414A-414D such that the upper surface 430F of the replacement element 430 is generally coplanar with the outer surface 413 of the airfoil. Hence, the replacement element 430 is assembled and secured to the airfoil 412.

After the assembly process of the replacement element 430 to the airfoil 412, the replacement element 430 is further secured to the airfoil 412 via a conventional brazing, diffusion bonding, e.g., transient liquid phase bonding, or welding process. Alternatively, the brazing, diffusion bonding or welding process may also be effecting during the process of assembling the replacement element 430 to the airfoil 412. In either case, the brazing, diffusion bonding or welding process also serves to seal any gaps surrounding the replacement element 430.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

What is claimed is:
 1. A process for repairing an airfoil structure adapted for use in a gas turbine engine comprising: providing an airfoil structure having a section with a defect; removing airfoil structure material comprising said section with the defect such that a through hole is created; providing a replacement element; providing interlocking structure; positioned said replacement element relative to said through hole; and securing said replacement element to said airfoil structure via said interlocking structure such that said through hole is covered.
 2. The process as set out in claim 1, wherein said removing comprises forming a through hole comprising a first outer section and a second inner section, said first section having a diameter greater than said second section.
 3. The process as set out in claim 2, wherein said replacement element comprises a first outer portion and a second inner portion, said first portion having a diameter slightly less than said diameter of said through hole first section and said second portion having a diameter slightly less than said diameter of said through hole second section, wherein said first outer portion is received in said through hole first section and said second portion is received in said through hole second section.
 4. The process as set out in claim 3, wherein said interlocking structure comprises threads on said replacement element and a section of said airfoil structure adjacent said through hole.
 5. The process as set out in claim 4, further comprising sealing said replacement element to said airfoil structure.
 6. The process as set out in claim 3, wherein said interlocking structure comprises a pin positioned through said replacement element and a section adjacent said through hole.
 7. The process as set out in claim 6, further comprising sealing said replacement element and said pin to said airfoil structure.
 8. The process as set out in claim 6, wherein said pin is threaded.
 9. The process as set out in claim 6, wherein said pin is positioned at a non-orthogonal angle to an outer surface of said replacement element.
 10. The process as set out in claim 1, wherein said airfoil structure comprises a vane or a blade.
 11. The process as set out in claim 1, wherein said replacement element comprises a main body portion and said interlocking structure comprises at least one tongue extending from said main body portion and further comprising forming at least one groove in a section of said airfoil structure adjacent said through hole, said tongue being adapted to be received in said groove.
 12. The process as set out in claim 11, wherein said interlocking structure comprises first, second, third and fourth tongues extending out from said main body portion and said forming comprises forming first, second, third and fourth grooves in said section adjacent said through hole.
 13. The process as set out in claim 12, wherein said first, second, third and fourth tongues have curved shapes and said first, second, third and fourth grooves have curved shapes.
 14. The process as set out in claim 13, wherein said positioning comprises positioning said replacement element upside down relative to an outer surface of said airfoil structure and said securing comprises rotating said replacement element 180 degrees such that said first and second tongues move through said third and fourth grooves and then into said first and second grooves and said third and fourth tongues move into said third and fourth grooves when said first and second tongues move into said first and second grooves.
 15. A repaired airfoil structure comprising: an airfoil structure having a through hole formed therein so as to remove a section with a defect; a replacement element positioned in said through hole; and interlocking structure to mechanically couple said replacement element to said airfoil structure.
 16. The repaired airfoil structure as set out in claim 15, wherein: said through hole comprises a first outer section and a second inner section, said first section having a diameter greater than said second section; and said replacement element comprises a first outer portion and a second inner portion, said first portion having a diameter slightly less than said diameter of said through hole first section and said second portion having a diameter slightly less than said diameter of said through hole second section, wherein said first outer portion is received in said through hole first section and said second portion is received in said through hole second section.
 17. The repaired airfoil structure as set out in claim 15, wherein said interlocking structure comprises threads on said replacement element and a section of said airfoil structure adjacent said through hole.
 18. The repaired airfoil structure as set out in claim 15, wherein said interlocking structure comprises a pin positioned through said replacement element and a section adjacent said through hole.
 19. The repaired airfoil structure as set out in claim 18, wherein said pin is threaded.
 20. The repaired airfoil structure as set out in claim 19, wherein said pin is positioned at a non-orthogonal angle to an outer surface of said replacement element. 